The present invention relates to clock generators generally and, more particularly, to a clock generator with programmable modulation to reduce EMI.
Clock generators are used to generate frequencies used by a variety of devices. When clock generators generate high frequencies (e.g., frequencies created over 100 MHz) high amounts of electromagnetic interference (EMI) may be generated. If the amount of EMI is too high, additional problems, such as data integrity issues, may be introduced in storage devices such as memories. It is therefore desirable to reduce the total amount of EMI generated by a clock generator circuit.
The present invention concerns an apparatus comprising a first circuit and a second circuit. The first circuit may be configured to generate an output signal that ramps between a first and second frequency in response to (i) a first control signal, (ii) a second control signal, and (iii) a first reference signal. The second circuit may be configured to generate the first and second control signals in response to a third control signal having a third frequency. The third frequency may reduce electromagnetic interference generated by the first circuit or devices connected to the first circuit.
The objects, features and advantages of the present invention include providing a circuit that reduces EMI through use of a clock generator with a programmable two-tone modulation that may be implemented in devices such as a phase-locked loop (PLL).